FRPs

Fiber-reinforced polymers (FRPs) are composite materials in which a polymer matrix binds and reinforces reinforcing fibers, typically glass (GFRP), carbon (CFRP), or aramid fibers. The matrix can be thermoset (such as epoxy, polyester, or vinyl ester) or thermoplastic, while the fibers provide most of the strength and stiffness. Fiber orientation and the reinforcement volume fraction determine mechanical properties, and FRPs exhibit anisotropic behavior with properties strongest along the fiber direction.

FRPs offer high strength-to-weight ratios, good corrosion and chemical resistance, and design flexibility. They can be formed into complex shapes and tailored for specific stiffness, strength, and impact requirements. Limitations include sensitivity to temperature and moisture for some matrices, variable fire performance, aging from ultraviolet exposure, and potential difficulties in repair. End-of-life disposal and recycling are ongoing considerations, especially for thermoset FRPs. Costs, particularly for carbon fibers, and the need for specialized processing equipment are also factors in selection.

Common manufacturing methods encompass hand layup, spray-up, filament winding, pultrusion, resin transfer molding (RTM), and vacuum-assisted resin infusion (VARI/VARTM). The main FRP classes are glass-fiber-reinforced polymer (GFRP), carbon-fiber-reinforced polymer (CFRP), and aramid-fiber-reinforced polymer (AFRP). Each class offers a different balance of cost, density, stiffness, and strength.

Applications span aerospace, automotive and rail components, construction and civil engineering (including FRP-reinforced sections and FRP rebars), wind turbine blades, marine equipment, and sports gear. In civil engineering, FRPs are valued for lightweight, corrosion resistance, and for retrofitting or replacing steel components in aggressive environments.